Recently with improvements in magnetic recording, there has been a growing demand for a high image quality and a high audio quality. To meet such demand, ferromagnetic particles are pulverized and magnetic flux density of the magnetic recording medium is increased. Also, an increased consumption of a magnetic recording medium may require that it is inexpensive. A magnetic recording medium comprising plural magnetic layers have been proposed to achieve the foregoing requirements, because an upper magnetic layer can provide characteristics for a high image quality, and a lower magnetic layer can provide characteristics for a high audio quality, thereby causing suitable ferromagnetic particles for each to be used. Further, the use of plural magnetic layers results in reduced costs because suitable materials can be used depending on desired characteristics of each of the plural layers. In order to attain a high image quality and a high audio quality, it is required to increase electromagnetic characteristics, particularly Rf output, to decrease noise, and to increase S/N.
To this end, it is required to increase the number of ferromagnetic particles per volume by making ferromagnetic particles small. However, even if the specific surface area of ferromagnetic particles is increased to increase the number of ferromagnetic particles per volume, it is difficult to attain the above object because holes are formed in the surface of ferromagnetic particles so that the size of ferromagnetic particles is not substantially reduced, and the ratio of the long axis to the short axis of ferromagnetic particles is reduced.
Namely, there are problems that when holes are formed in the surface of ferromagnetic particles, the loss of magnetic ratio increases, and when the long axis/short axis ratios are reduced, the orientation property of ferromagnetic particles is deteriorated at the time of the manufacture of a magnetic recording medium.
When ferromagnetic particles are made small, there is a further problem that the transfer characteristics are deteriorated due to the increase of components with a low coercive force, thus making the ferromagnetic particles impractical.
To overcome the above problems, JP-A-63-187419 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes plural magnetic layers in which an average length in the long axis of ferromagnetic particles contained in an uppermost magnetic layer is less than 0.25 microns, a crystallite size of the ferromagnetic particles contained in the uppermost layer is less than 300 .ANG. as measured by X-ray diffraction, an average length in the long axis of ferromagnetic particles contained in magnetic layers other than the uppermost layer is 0.25 microns or more, and a crystallite size of the ferromagnetic particles contained in the magnetic layers other than the uppermost layer is 300 .ANG. A or more.
The present inventors have found that when such plural magnetic layers are used in a video tape of VHS or beta type, Hc (i.e., coercive force) of an upper magnetic layer is preferably 650 to 1000 Oe, and Hc of a lower magnetic layer is preferably 0.6 to 1.0 times that of the upper magnetic layer.
However, it has been found that when ferromagnetic particles contained in a lower magnetic layer, having an average length in the long axis of 0.25 microns or more are used, noise at the short wave length region is increased, S/N is widely decreased, the surface property of the magnetic layer is deteriorated, and also Y-S as well as Y-S/N are decreased.